8 replies to this topic

[Tom Hampton]

Ok, next issue from last weekend. I have a buzzing sound coming from the trans tunnel. Occurs in gears 1-4, i didn't have much time to play with 5 so I'm unsure.

The noise can be felt in the gear shifter. It goes away with enough throttle to add acceleration load. I'm thinking u-joint. Given these conditions it seems like u-joints, but my previous experience with that part has been a lower rate of vibration... not really what would be called a buzz. Also it doesn't seem to be related to road speed.

My other thought is clutch disk. I have the ACT unsprung disk. Could the tranny input shaft rattle in the disk hub? Still, doesn't seem to fit with reverse loads during decel.

[Keith Novak]

The 1st and easiest thing to look at is your exhaust. Due to all the fitment issues people have with the SD, it can rattle against the stub axles by the diff (making a big stinking hole in the exhaust ) and it can make more of a buzz contacting the lap belt bolt that sticks out of the trans tunnel. If it's close to the stub axle, adjust it for sure (see also big stinking hole). If it makes the noise with the car running, at idle grab the tip of the exhaust with your hand and see if it goes away. If it does, definately look at how close it is to that bolt.

[Tom Hampton]

Still have stock exhaust. But, i will look for any things that might be rattling or making contact under reverse torque.

[dmathias]

You may have a different issue, but if this is the first time you've driven a car with all the sound deadening/carpet removed you'll hear all sorts of noises.

[Tom Hampton]

It's actually the fourth time on track. But, i can't say if I'd heard this noise before. That's why I'm asking. Perhaps it is normal.

[dmathias]

Check nuts and bolts for tightness, check any heat shields, check the heat shield on the down tube - the spotwelds break and it makes an annoying rattle, check the yolk on the front of the differential - if it wobbles the rearend is a goner. Noises like this are notorious for 'traveling', that is, they sound like they're coming from one place but are really transmitted from somewhere else.

[Alberto]

I had vibrations too shortly after completing my build in Jan. Check:

1. The stock downpipe often has a "bracket" of sorts around it near where the engine and trans meet. It is supposed to bolt onto another bracket that is attached to 2 bolts on the trans-to-engine mate. If the bracket on the downpipe is twisted a bit it won't be happy and buzz like a mofo.
2. The bracket that attaches the clutch line to the firewall. If it is loose, it will buzz and rattle.
3. The bracket on the wiring harness that attaches the wiring harness to the trans/engine.

All 3 were loose on mine and I incorrectly thought I had screwed up my first ever clutch install on my car. I'm using the stock cat and exhaust as well fyi. I haven't spent the $$ on a performance exhaust yet. Waiting on my sponsorship package...

[Tom Hampton]

Still havent located this noise. Happens in 1-4th gear between 2500 and 4000 rpm. It is not road SPEED dependent. It is particularly prevalent under deceleration. I can't hear anything when in 5th gear...although road/wind noise is pretty high at that speed 75+. If it were road-speed dependent, I'd think it was the drive-shaft/u-joints.

I know these things can travel, but it sounds like its coming from the bell-housing. Further, I can manipulate the noise by modulating the throttle---there is a tipping point of just barely cracking the throttle to stop deceleration that will make the noise go away. Sometimes the noise is present under acceleration, too. It seems like its the clutch disk rattling on the transmission input shaft. I've have a solid clutch-hub, which I've never driven before. Is it possible that it is what is making the noise? If so, is that "normal" for a solid/unsprung hub?

I've also heard mention on miata.net of a transmission gear lash "known issue" with the miata transmission.

Thoughts?

[JayF]

Tom, throw a SD exhaust on and you'll never notice those sounds again. I did the first test drive of mine today around the neighborhood and I it's definitly loud.